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Mon, 22 Dec 2025 03:42:02 +0000 (UTC) Received: from localhost (unknown [10.72.112.76]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2FD561800664; Mon, 22 Dec 2025 03:41:58 +0000 (UTC) Date: Mon, 22 Dec 2025 11:41:55 +0800 From: Baoquan He To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , Barry Song , Chris Li , Nhat Pham , Yosry Ahmed , David Hildenbrand , Johannes Weiner , Youngjun Park , Hugh Dickins , Baolin Wang , Ying Huang , Kemeng Shi , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 15/19] mm, swap: add folio to swap cache directly on allocation Message-ID: References: <20251220-swap-table-p2-v5-0-8862a265a033@tencent.com> <20251220-swap-table-p2-v5-15-8862a265a033@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Stat-Signature: gwkpwt5ci1krxhtf9hfwzuzif34pxoid X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 71037A000C X-Rspam-User: X-HE-Tag: 1766374930-300789 X-HE-Meta: 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 9z4Tf/p8 /9chTYELysYpXgLDDkXWZFetiQalRQQT7TnVc28I5kmAtoCYH5RarEp9Yifgl3xXKr2XFdbglsG4fXI7gZgk/NSMPHpqeR0oTyX8ACXUjf04xYnyAdLAig0by4hBU2IB5qMeS8XYmJUjavSPRO8LUeJ0zoIU5eMy+5HsfMv8jp/NGUVNQcOjMvY11rUs/YZ7+LpqHfJkF3mi3kVSvKdsr5zMemiLyY0pA4SJlCr9bbUKB0FQMDLIj6E59mg5RMNDiNyaStUC8SgpDO/pmVk1FZmPMfKXhUJfAWYuWmAGXxiiNvahdj/6SaLydPcgygVVvGPXRz9QaKNgVgYabMVuFfDouLX70cudkKqr6o+BYUz0kgfotctcd4qgKUmL76XCFI23/wVBCcm+RDygLQlwBvBy/+TX/GQe3VpKyspEoEQJ2ziosM+OS6xrcm2Vr+ab08yJMY1X6oHgzF6GvmU1FixcRxFWouTVUiwBR X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/22/25 at 10:42am, Kairui Song wrote: > On Sat, Dec 20, 2025 at 12:12 PM Baoquan He wrote: > > > > On 12/20/25 at 03:43am, Kairui Song wrote: > > > From: Kairui Song ...snip... > > > diff --git a/mm/swap_state.c b/mm/swap_state.c > > > index 327c051d7cd0..29fa8d313a79 100644 > > > --- a/mm/swap_state.c > > > +++ b/mm/swap_state.c > > > @@ -122,35 +122,56 @@ void *swap_cache_get_shadow(swp_entry_t entry) > > > return NULL; > > > } > > > > > > +void __swap_cache_add_folio(struct swap_cluster_info *ci, > > > + struct folio *folio, swp_entry_t entry) > > > +{ > > > + unsigned long new_tb; > > > + unsigned int ci_start, ci_off, ci_end; > > > + unsigned long nr_pages = folio_nr_pages(folio); > > > + > > > + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); > > > + VM_WARN_ON_ONCE_FOLIO(folio_test_swapcache(folio), folio); > > > + VM_WARN_ON_ONCE_FOLIO(!folio_test_swapbacked(folio), folio); > > > + > > > + new_tb = folio_to_swp_tb(folio); > > > + ci_start = swp_cluster_offset(entry); > > > + ci_off = ci_start; > > > + ci_end = ci_start + nr_pages; > > > + do { > > > + VM_WARN_ON_ONCE(swp_tb_is_folio(__swap_table_get(ci, ci_off))); > > > + __swap_table_set(ci, ci_off, new_tb); > > > + } while (++ci_off < ci_end); > > > + > > > + folio_ref_add(folio, nr_pages); > > > + folio_set_swapcache(folio); > > > + folio->swap = entry; > > > + > > > + node_stat_mod_folio(folio, NR_FILE_PAGES, nr_pages); > > > + lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr_pages); > > > +} > > > + > > > /** > > > * swap_cache_add_folio - Add a folio into the swap cache. > > > > With my understanding, __swap_cache_add_folio() is the pure > > functionality of adding a folio into swap cache. While > > Hi Baoquan, thanks for the review and suggestion! > > > swap_cache_add_folio() is specifically adding a folio into swap cache > > during swap in path. Not sure if we can rename them to reflect this > > clearer. At least from the functiona name and below kernel doc we can't > > feel that. Maybe: > > __swap_cache_add_folio() -> swap_cache_add_folio() > > The `__` prefix should stay, I think. This function requires the > caller to lock the swap cluster. > > > swap_cache_add_folio() -> swap_cache_add_swapin_folio() > > Indeed, my plan is that `swap_cache_add_folio` will be gone soon, we > should always call `swap_cache_alloc_folio` instead to do the swap > folio allocation in a unified way, and just remove this. > > Currently we can't do that because shmem and anon have different > routines for swapin folio allocation. Having a unified > `swap_cache_alloc_folio` will provide better swapin fallout control > and cleaner cgroup charging to avoid thrashing, etc. > > Also this helper is currently inexplicitly used by zswap writeback > too, so adding the swapin keyword seems not accurate. OK, sounds good to me. Thanks for detailed explanation.